DHT and pattern hair loss

Key takeaways

• DHT is needed for male pattern baldness. Men born without working 5-alpha-reductase type 2 rarely go bald, and blocking DHT with finasteride stops or reverses loss in most men. Kaufman 2002; Azzouni 2012; Kaufman 1998
• Genes decide which follicles respond. Heritability is high (79% in elderly Danish twins, 62% from UK Biobank relatives), and hundreds of genetic loci are involved, including the androgen receptor gene on the X chromosome. Rexbye 2005; Yap 2018
• "It comes from your mother's side" is only partly true. The receptor gene sits on the X chromosome, but X-chromosome loci explain only about 12% of the genetic signal; most risk comes from chromosomes inherited from both parents. Yap 2018
• The same hormone grows beards and shrinks scalp follicles, because follicles at different body sites answer androgens with different signals. Randall 2000; Inui 2013
• It is progressive. Untreated young men in placebo groups lost 26% of crown hair density over 5 years, and 75% looked worse. Kaufman 2008
• It is common: about 50% of men by age 50 Pirastu 2017 and nearly half of women over a lifetime. Kearney 2026
• Inflammation adds to the picture. Bald scalp has raised prostaglandin D2, and many treatment-resistant patients show inflammation and scarring around follicles on biopsy. Garza 2012; Umar 2026
• Women's pattern loss differs. Its molecular basis is undetermined, male risk genes are not clearly shared, and finasteride 1 mg failed in postmenopausal women. Liu 2025; Redler 2017; Price 2000

Testosterone, DHT and the 5-alpha-reductase enzymes

5-alpha-reductase converts testosterone into DHT. DHT binds the human androgen receptor about 2-fold more tightly than testosterone and lets go about 5-fold more slowly, which makes it the stronger signal at normal concentrations. Grino 1990

• Two main enzymes: type 1 is active in skin from puberty onward, while type 2 dominates in genital skin and prostate and is briefly active in newborn scalp. The authors proposed type 2 as an initiating factor in male pattern baldness. Thigpen 1993 Hair follicles contain both enzymes, androgen receptors and receptor co-activators. Inui 2013 A third type exists. Leliefeld 2025
• Bald scalp is rich in DHT: 7.37 vs 4.20 pmol/g in hair-bearing scalp of the same men, while testosterone did not differ. Dallob 1994
• Natural experiments:
  • Men with inherited type 2 deficiency (first described in 1974 in a Dominican kindred) have low DHT, partly virilise at puberty, and "male pattern baldness and acne develop rarely". Imperato-McGinley 1974; Azzouni 2012
  • Eunuchs with low testicular androgen also implicate androgens, and DHT in particular, as necessary for male pattern loss. Kaufman 2002
  • Men with Kennedy disease, whose androgen receptor works less well, had thicker hair and no age-related rise in balding scores. Sinclair 2007
• Drug evidence: finasteride lowers scalp DHT by about 60 to 70% and improves hair in controlled trials. Drake 1999 Dutasteride, which also blocks type 1, works better still. Gubelin Harcha 2014

Genetics and heritability

• Twins: in 148 intact pairs of Danish twins aged 70 and over, heritability of balding was 79% (95% CI 40 to 85%). Rexbye 2005
• UK Biobank (205,327 men): pedigree heritability 0.62, SNP heritability 0.39, 624 near-independent loci; 26 X-chromosome loci explain 11.6% of SNP heritability. Yap 2018
• Other large studies: 63 loci explaining about 39% of variance Heilmann-Heimbach 2017; 71 loci explaining 38% of risk Pirastu 2017; more than 250 loci and a genetic predictor that separated no loss from severe loss with an AUC of 0.78 (positive predictive value 59%). Hagenaars 2017 A 2025 review counts more than 380 loci, including androgen and WNT pathway genes. Liu 2025
• The receptor gene: a variant near it was found in 98.1% of young bald men vs 76.6% of non-bald men. Ellis 2001
• Androgen-independent routes exist: the chromosome 20p11 locus showed no interaction with the receptor locus. Hillmer 2008

Why the scalp shrinks while the beard grows

• After puberty, androgens turn tiny vellus follicles into large terminal ones in the beard and armpit, do nothing to eyelashes, and do the opposite on the balding scalp. Androgens act mainly through the dermal papilla, the cluster of cells at the follicle's base. In culture, androgens raised the growth-promoting output of beard papilla cells but lowered that of balding scalp cells, and the differences are thought to be set during embryonic development. Randall 2000
• Androgens induce IGF-1 (a growth signal) from beard papilla cells and TGF-beta1, TGF-beta2, DKK-1 and IL-6 (inhibiting signals) from balding papilla cells. Inui 2013 Androgen-induced TGF-beta1 halved keratinocyte growth in co-culture Inui 2002, and DKK-1 pushes follicles into regression in mice. Kwack 2012
• Balding papilla cells carry more androgen receptors than non-balding ones (0.06 vs 0.04 fmol per 10,000 cells). Hibberts 1998
• Follicles at the back of the scalp resist androgens, which is why they are used as transplant donors. Liu 2025
• What this means for you: baldness is mostly about how sensitive your follicles are, not how much testosterone you have. In the same men, bald and hairy scalp had the same testosterone but different DHT. Dallob 1994

Miniaturisation and the hair cycle

• Pattern hair loss is a progressive shortening of the growth phase with each cycle, plus miniaturisation that converts thick terminal hairs into fine, short, vellus-like ones. van Zuuren 2016; Kearney 2026
• Miniaturisation is partly reversible while follicles remain: dutasteride cut the count of thin hairs from 65 to 57 per cm² over 24 weeks. Shanshanwal 2017
• In placebo groups, men lost 239 hairs (26.3%) in the target area over 5 years. Kaufman 2008

Inflammation, scarring and prostaglandin D2

• Prostaglandin D2 and its synthase are higher in bald than in haired scalp, and PGD2 inhibits human follicle growth through the GPR44 receptor. Garza 2012
• In 129 referral-centre patients, 81% had lymphocytic inflammation and scarring around the upper follicle, more often in men 44 and over, those at Norwood stage 5 or higher, and poor responders. Adding anti-inflammatory treatment was associated with better outcomes, but the study was retrospective, from one centre, and had no control group. Umar 2026
• Testosterone raised TGF-beta1 and collagen production in scalp fibroblasts in vitro, and finasteride blunted this. Yoo 2006

How women's pattern loss differs

• Mechanism: "the molecular basis of AGA in women remains undetermined". Liu 2025 Androgens probably matter in some women, but the evidence is weaker than in men, and candidate-gene studies have not found clear loci. Redler 2017 A Korean genome study found sex-specific signals (FZD1, GJC1) in women. Lee 2024
• Drug response: finasteride 1 mg did nothing in postmenopausal women Price 2000, and the Cochrane review found it no better than placebo in women (low-quality evidence). van Zuuren 2016 The original trial authors concluded that male and female pattern loss are distinct clinical entities. Kaufman 2002
• Pattern: diffuse thinning over the mid-frontal scalp, where the frontal hairline may or may not be preserved. van Zuuren 2016; Won 2018
• Treatment: only topical minoxidil is FDA-approved for women, and antiandrogens such as spironolactone are used off-label. Kearney 2026 See spironolactone, cyproterone acetate, bicalutamide, flutamide and oral contraceptives.

What it means for your hair

• Curl pattern, porosity and thickness do not change the biology. Fine or low-density hair shows thinning earlier because miniaturisation is more visible.
• Sex and age: men typically show temple recession and crown loss; women show diffuse central thinning. Women with hair loss plus acne, excess facial or body hair, or irregular periods should see a doctor to check for excess androgens.
• Family history is strongly predictive, through both parents. Yap 2018
• Ancestry: prevalence and patterns vary substantially between ancestries. Liu 2025

Myths and facts

• "Baldness comes from your mother's father." Partly. The receptor gene is on the X chromosome, but most genetic risk sits on chromosomes from both parents. Yap 2018
• "Bald men have more testosterone." Not shown. Androgens are necessary, but follicle sensitivity decides who balds. Dallob 1994; Hibberts 1998
• "DHT is just bad." DHT builds male genitalia, the prostate and the beard; men without the type 2 enzyme have sparse beards. Azzouni 2012
• "Hair loss is normal ageing, so do nothing." In young men it is progressive and treatable; untreated men lost about a quarter of crown density in 5 years. Kaufman 2008
• "Female hair loss is the same as male, so male drugs work." Finasteride 1 mg failed in postmenopausal women. Price 2000

Fun facts

• Red deer stags grow a mane each breeding season; androgen receptors were found in papilla cells from mane follicles but not flank follicles. Randall 1993
• Men with Kennedy disease, a rare neuromuscular disorder that weakens the androgen receptor, keep thicker hair with age. Sinclair 2007

Bottom line

Think of pattern hair loss as genetically sensitive follicles plus DHT plus time. Early action preserves more hair, because treatments mainly halt progression and only partly reverse miniaturisation. For men with a family history and early recession or crown thinning, DHT-lowering treatment (finasteride, then dutasteride) is the evidence-based core. For women, diagnosis comes first, and male DHT blockers are not first-line. Inflammation is an emerging explanation for non-response, not established fact. Discuss with a doctor.